amir abdullah

In recent years, the use of various polymer composites in the aerospace, marine, and automotive industries have expanded due to their low weight and high mechanical strength. Due to hard phases and layered-type material structure, problems like poor surface quality, high cutting forces, and severe tool wear occur in the drilling of carbon fiber reinforced composites. A method that can reduce the mentioned effects in CFRP drilling is using ultrasonic waves in the drilling. In this paper, the idea of using a non-rotating vibratory tool ultrasonic method for drilling CFRP has been introduced and the effect of exerting ultrasonic waves on non-rotating drilling tool has been studied. The composite specimens were prepared by the layering method under load. The design of experiments using the Taguchi method was carried out, the optimal drilling parameters were determined, and the effects of ultrasonic on the surface roughness, surface quality (delamination, cracks, un-cut fibers), and cutting forces were investigated. The results indicated that ultrasonic waves in CFRP drilling could significantly reduce surface roughness (up to 49% surface roughness improvement) and the average axial force could decrease up to 57% compared with the condition that no ultrasonic waves have applied. Delamination of the drilled surface also decreased with the use of ultrasonic waves. This indicates that the idea of non-rotating ultrasonic tool can have similar effects as a rotating ultrasonic tool in drilling CFRPs.

Machining of hardened steels, which their hardness is generally higher than 45 Rockwell C, is called hard turning. These components usually work under dynamic loading conditions and require a high level of surface finish (in the order of 0.15 μm Ra) which cannot be achieved by sequential hard turning and burnishing processes. However, there are serious concerns about this complimant grinding operation; grinding process, on one hand increases tensile residual stresses and on the other hand, increases crack nucleation regions. Therefore, these two factors might decrease workpiece fatigue strength. So, in this paper, the effects of adding a grinding operation before ball burnishing process, have been experimentally studied on final surface roughness and burnishing forces; at the same time, in order to consider the possible destructive effects of grinding process, a set of experimental measurements including surface residual stresses and endurance limit measurement, have been done for AISI 4130 fatigue samples. Based on the achieved results, adding a grinding operation before burnishing process, has lead to 91.56% improvement in surface finish and 39.52% reduction in burnishing forces. In addition, surface residual stress are compressive and there is slight difference in the magnitude of compressive residual stresses in comparison to burnished hard turned samples. Due to these positive findings, endurance limit of produced samples show 10.95% improvement in comparison to burnished hard turned samples.

Indentation forming is an internal tube forming process in which a mandrel with a diameter slightly larger than that of the tube is pressed inside the tube and in so doing, creates the internal profile. Forming forces have a significant effect on the spring back, residual stress, quality of the inner surface, quality of tube dimensions, and tool wear. In this study, the forming process of CK45 steel tube by carbide tungsten tool in the presence of ultrasonic vibration has been simulated and the effect of ultrasonic on the forming mechanism has been investigated by introducing two regimes according to the forming conditions. The effects of tool feed-speed and amplitude of vibration on forming force reduction have been investigated. According to the simulation results, the main reason for the force reduction in the presence of longitudinal tube ultrasonic vibration is the intermittent phenomenon which is the continuous or impulsive regime. The critical amplitude which determines the borderline of continuous and impulsive regimes is obtained 38µm by the simulation of the process. The maximum force reduction obtained in continuous regime is 64.2% at the critical amplitude. The simulation results are consistent well with the previous experimental data.

Hot pressing of metal powders is used in production of parts for similar properties to wrought materials. Since residual porosity, inhomogeneous properties, dimensional and geometrical instability and therefore reduction in mechanical strength are the main problems in powder metallurgy components which are due to friction between powder particle interfaces and powder compact and die walls. Because of this, access to parts with high density and homogeneous structure is the great object in powder metallurgy. One of the remedies can be employment of ultrasonic vibrations which is thought to result in increased rates of densification and therefore higher efficiency of the process in increase of part density and strength. To evaluate this solution, this paper deals with the effects of high power longitudinal ultrasonic vibrations on the densification of AA1100 aluminum and Ti-6Al-4V titanium alloy powder under constant applied stress and different temperatures. The effects of powder type and process temperature on the densification behavior and ultrasonic efficiency are discussed. For experimental tests, setup of ultrasonic assisted hot pressing of powders were designed and fabricated. The results show that applying ultrasonic vibrations leads to obtaining higher relative density. In addition, it is found that the effect of ultrasonic vibrations is greater for Ti-6Al-4V powders. However, the temperature has different effects on the ultrasonic vibrations efficiency in two types of powders.

Metal forming is a conventional manufacturing process that a material with simple form is subjected to plastic deformation and emerged to industrial end products. Reduction of forming forces and improving of products quality have been a promising object for investigators and artisans. To accede this purpose, primary methods such as increasing material temperature and modern methods such as use of high power low amplitude ultrasonic vibrations were introduced. In ultrasonic assisted forming, high power ultrasonic transducer produces low amplitude high frequency mechanical vibrations which transmitted to material subjected to deformation and contacting surfaces of tool/workpiece. Results show reduction of forming forces and tool wear as well as improving surface integrity and dimensional stability that lead to increasing production rate and process efficiency. By regarding to importance and capability of ultrasonic assisted metal forming, this paper is concerned with application of ultrasonic vibration on metal forming processes. To this purpose, fundamental and mechanisms of application of high power ultrasonic were introduces and discussed. Also, industrial future of this technology as well as its advantages, range of application and its restriction were mentioned.

The increased material removal rate in ultrasonic-assisted wire electrical discharge turning (by∼2 times)was attributed to compressive and rarefying wave front in dielectric and discharge column sliding into plasma channel and molten crater due to applying lateral ultrasonic vibration on the wire. A single discharge was analytically and experimentally studied and the effective forces and factors on plasma channel including Lorentz force¡ increase of pressure and surrounding vapor ionization of plasma channel¡ elongation of molten crater due to lateral displacement of wire and creation of positive and negative pressures of the ultrasonic wave on molten crater were investigated. Experiments were performed in different machining parameters of voltage and power with and without ultrasonic vibrations. By using ultrasonic vibration¡ the plasma density was increased due to decrease of bubble growth. The current density was increased and pressure drop in the end of discharge was increased. As a result¡ a great amount of the material was exploded out of the crater due to bulk boiling. The plasma channel sliding was elongated the molten crater on workpiece surface¡ which leads to material removal increase.

Reduction of cutting force in a machining process offers several advantages including increase in tool life, and improvement in the quality of the machined surface. One the new techniques for reducing cutting force relates to ultrasonic vibration assisted machining. In the present paper, one-dimensional ultrasonic vibration-assisted side milling process of Al7022 aluminum alloy has been studied. In order to investigate the effect of cutting speed, feed rate, radial depth of cut, and vibration amplitude on three cutting force components and their resultant, a special experimental setup has been designed and established which applies one dimensional ultrasonic vibration to work piece. Applying the ultrasonic vibrations on milling process, affects mostly on feed component of cutting force which is unidirectional with the work piece vibration, and decreases it by 33.5% in average. Decrease in cutting speed and increase in vibration amplitude, results to increase the separation of tool and work piece from each other in a portion of each vibration cycle, and larger decrease of the feed force. The average decrease of the resultant cutting force in ultrasonic-assisted milling process is 10.8%.

Incremental Sheet Metal Forming (ISMF) is based on localized plastic deformation. In this process, a hemispherical-head tool, controlled by a CNC milling machine, shapes a sheet metal according to a defined path. Study of the forming force is one of the most important topics in this process. Increasing of vertical step size, tool diameter, wall angle and sheet thickness together with using of high strength sheet metals and lightweight alloys, leads to an increase in the forming force. In this paper, the performance of a novel forming process, named Ultrasonic Vibration assisted Incremental Sheet Metal Forming (UVaISMF) has been investigated. The procedure of design, manufacture and test of vibratory forming tool, is presented. The occurrence of longitudinal mode and resonance phenomenon has been confirmed by the results of modal analysis and experimental test. Furthermore, the effect of ultrasonic vibration on the vertical component of forming force and spring-back has been studied. Aluminium sheet of grade Al 1050-O is used as a work material. Experimental results obtained from straight groove test, indicate that ultrasonic excitation of forming tool, will reduce the average of vertical component of forming force and spring-back in comparison to conventional process.

Calculation the cutting force in machining processes is of great importance. In this paper، undeformed chip thickness in one-dimensional ultrasonic vibration assisted milling is calculated and then، a model for determining the cutting force in this process is presented. Analytical relations show that in ultrasonic assisted milling (UAM)، the maximum cutting force is greater than in conventional milling (CM)، but the average cutting force is decreased. To verify the proposed relations، with the aid of a particular experimental setup، one-dimensional vibration in feed direction is applied to workpiece and cutting force in CM and UAM is measured experimentally. Greater maximum cutting force in UAM and decrease of average cutting force in UAM compared to CM is observed experimentally as well. Comparison of average values of cutting force shows that the analytical relations for predicting the cutting force have 16% average error in CM and 40% average error in UAM. Given that the analytical calculation of undeformed chip thickness and cutting force in UAM and also comparison of experimental forces with the modeled ones has been done in this paper for the first time، the accuracy of proposed relations are acceptable.

Wire electrical discharge machining (wire-EDM) has a significant position among production technologies mainly due to its capacity of machining hard materials and intricate shapes. One of the major problems with this process is the error in cutting corners. Processing forces acting on the wire and low rigidity of the wire are responsible for wire deformation، which has a direct influence on the accuracy of the corner cutting. In this research، investigation is focused on the convex corner radii errors and alternative solutions are proposed for the case of successive cuts (one roughing and two finishings). Experiments are carried out for roughing operation by considering frequency of discharges and feed speed. The residual materials on straight and curved paths are the output parameters. Results indicate that optimization of these parameters have a better influence for control of residual material thickness on straight paths than on curved corners. One important conclusion is that roughing is the most influential stage of cutting by WEDM. Then، concave corner radii produced during successive cuts، the effect of corner angle and corner radii are investigated. Errors at radii of different corner angles are identified and related to arc length and residual material thickness in the curved corner. Finally، an effective approach is presented for improving the accuracy of the small-radius concave corner radii of finishing stage. The main conclusion is that to achieve accurate corner radii، one must increase the traversed corner arc length by wire in the small-radius concave corner radii.

As for spray-guided direct injection gaseous fueled engines, a few time is available for mixture preparation, exact determination of the gaseous jet characteristics emanating from the injector is very important. The main purpose of the present work is investigation of the effects of pressure and density ratios on the multi hole gaseous jet tip axial and radial penetration lengths and its velocity. For this, ultra high speed Schlieren imaging of the transient jet with high spatial and temporal resolution was utilized. jet images were analyzed using digital image processing method and the jet characteristics were extracted using an in house software which worked based on edge detection approach. Results revealed that regarding to the velocity curves, formation of the multi-hole gaseous jet is comprised of three stages of: emergence of the individual plumes, merging and penetration of the main spray. It was also found that changing the chamber gas density wouldn’t alter the maximum and minimum times in velocity curves and decreasing the density ratio of the injection gas to chamber gas would decrease axial penetration and jet tip velocity and increase jet spreading angle.

The aim of present study is to investigate the kinematics of tool-workpiece’s relative movement in conventional and ultrasonic-vibration assisted turning (UAT). The kinematic analysis of UAT shows that the movement of cutting tool edge relative to the workpiece resulted from the cutting speed, feed speed and tool’s vibration affects the lateral machined surface of workepiece and leaves a repeating pattern of crushed and toothed regions on it. This results in an increase in the surface hardness of the lateral machined surface in comparison with conventional turning (CT). A model of the tool-workpiece’s relative movement has first been developed in the present study. This model predicts a surface hardening effect for the lateral surface in UAT in comparison with CT. Several experiments were subsequently carried out employing a surface micro-hardness testing machine and an optical microscope to verify the predicted results.